Current and Historical Instantaneous Data Availability

The available parameters from the Current Conditions and
Historical Observations pages on the National Water Information System Web
Interface have two categories of instantaneous data availability. For some
parameters, historical data are available as far back as October 1, 1950,
whereas for others only the most recent 120 days of provisional data are
available. The period of availability depends on the intended use of the data and
can vary from site to site and/or between parameters at a site as described
below.

Available Historical Instantaneous Data:

Parameters with historical
instantaneous data are measured by the USGS Water Science Center (WSC) with the
intent to publish and are subject to a thorough review and approval process. Typically, these data have corresponding historical daily values available for the
period of record. These instantaneous data are limited to data collected since
October 1, 1950.

Data are presented as approved or PROVISIONAL as
appropriate, however provisional data will be provided for only the most recent
three years. In cases where data are not approved within a three year period,
interested users should contact the local WSC for further information.

Available Operational Instantaneous Data:

These parameters typically are
collected by the USGS for the purposes of supporting short-term operational
needs of the data network (for example precipitation at some locations) or parameters
measured to facilitate the computation of another parameter of interest (for
example, stage is used in the computations of streamflow). In either case,
these parameters are not necessarily corrected for errors or omissions either because
the short-term need for the operational data has passed or because other methods
were used to estimate the primary parameter of interest. Operational
instantaneous data typically are not intended for publication and therefore are
limited to the most recent 120 days.

Please note that the above designations are not uniformly
applied from site to site for a given parameter. For example, whereas stage
data at some sites are fully quality assured, published, and are historically
available, at other sites they are not quality assured and will only be
available for 120 days. The same site-to-site variations will exist for
precipitation and other parameters depending on the intended uses of the data.

Significant gaps in the availability of historical instantaneous data may exist due to instrument problems, environmental conditions or other factors that affect the ability to collect data. For some parameters, especially streamflow and others that are routinely estimated as necessary, a complete record may be available as Daily Data.